Al: One would also hope that there will be some voluntary removals of analog VHF systems to help with the transition. I don't hold out much hope for this, but it's probably a good excuse for a some repeater owners who didn't want to look like they were giving up, but have machines that get little to no use or little or no support from other Hams.
Yes, combining systems does work. This is another reason we're considering the dual UHF D-Star ports for our network. That not only provides the multiple simultaneous use you get with a VHF/UHF combination, but also permits common use of antennas. When you consider that the cost of duplexers and antennas for two bands is probably equivalent to having separate receive and transmit antennas with combiners and splitters for one band, and you consider the significant increase in system performance you can get if you don't duplex on the same antenna, it's pretty attractive. This also permits the use of a tower-mounted receive amplifier that will probably net you more that 10 dB receive performance improvement. In addition, it's simple to add more receivers and not too hard to add more transmitters without having to mess with any transmission lines or antennas, which could certainly be analog if desired. One of our systems here does exactly this with two UHF analog repeaters. The duplexer from one was pressed into service to combine one 25W and one 200W transmit signal at 1 MHz spacing (UHF). We have a tower mounted preamp at the receive antenna (Angle Linear) with front-end band filter which lets us use 500'+ of LMR-400 for the receive line (again a savings) and then have a distribution amp down at the equipment. We also combine the UHF transmit signals on the same line as the VHF repeater with TX/RX band combiners. All very robust and incredible sensitivity for the UHF systems. Considering the congestion on 2M, I wouldn't be surprised if multiple UHF D-Star ports become more common. Question though. How many UHF ports can you put on one controller or gateway? Chuck - N8DNX Al Wolfe wrote: > For number of reasons it usually much easier to put a D-Star system up > on UHF rather than VHF. VHF is much more crowded in most places and many > locations have no open VHF pairs. Attrition may eventually open up some > pairs but many places have long waiting lists. Attempts to move D-Star to > the front of the list will prove fruitless as it should be. It will also > alienate those already on the waiting lists. So forget about VHF D-Star > repeaters for the immediate future unless you're in Montana or North Dakota. > ( I can say that as I've lived both places.) > > There are many more MHZ on 440 than two meters, therefore, many more > pairs. With 25 kHz between channels a D-Star repeater on an offset can be > placed closer to an analog system with out causing problems. > > Another possibility is combining a D-Star system with an existing UHF > repeater's hardware. A frequency 300 to 500 kHz away from an exiting system > is easy to combine. I built up such a system here in eastern Illinois and it > works very well. The D-Star repeater shares the filters, feedline, and > antenna with an existing analog repeater and they play well together. Thanks > to ebay the combiner hardware set me back less than $300. YMMV on this, > though. > > I would consider combining a VHF D-Star and analog system but the > requirements on VHF are much more stringent with only 600 kHz between > receive and transmit. The combining hardware is a lot more difficult to find > as well. Also, in Illinois D-Star systems are only to be assigned to 145 > output frequencies so combining with an existing 146 or 147 system would > need at least another set of duplexers, a major expense. > > If someone is going to be using D-Star they're going to have to buy a new > radio. All but a couple (IC-2200 and IC-V82) are dual band so they've > already got the hardware to use UHF. Therefore, I recommend very seriously > considering UHF first when planning your first D-Star system. > > > Al, K9SI
